1. Field of the Invention
This invention relates to radio paging systems, and more particularly the invention relates to systems that implement an automatic mechanism for the confirmation of receipt of a paging message.
2. Discussion of Prior Art
The term "radio paging" refers to services in which messages, or "pages", are transmitted via radio, throughout a particular geographic area, to "pagers" in the possession of subscribers to this service. In the current art, these messages are broadcast digitally and contain short numeric (e.g. a phone number) or alphanumeric messages with length limitations on the order of tens of characters.
A representative architecture for a paging system is depicted in FIG. 1. A page is initiated by a telephone or computer modem call through a wide area network interface 1, typically provided by the local telephone company, to the paging service provider's offices. This initial call specifies the message content and the address of the pager for which the message is intended. A paging controller 2 transmits the information associated with each page, via paging control links 3 (a,b,c), to base stations 5 (a,b,c) serving the target pager's geographic area. Each base station is responsible for providing radio paging coverage throughout a particular paging cell. Cell boundaries 4 (a,b,c) are determined by regulatory limits on emitted radio frequency energy and by local propagation effects. Information on pager locations is not maintained by the system. Each page is therefore broadcast omnidirectionally by all base stations in the target pager's geographic area in an attempt to assure successful delivery of the page. Users equipped with pagers are identified by a boxed "U" in the figure. Pagers continually monitor the base stations' transmission frequencies, and, when a pager detects a message incorporating its own address, that pager receives the message and displays it, most usually on an integral liquid crystal display or similar device. FIG. 2 depicts a pager 7 with integral display 8 and control keys 9 (a, . . . ,d).
Radio paging, as described above, has the following three key deficiencies:
a) It is impossible for the paging system to determine whether or not a page has been received. A target pager might be outside the coverage area of the paging system, for example, or it might not be operating at the time that the page is transmitted.
b) Existing paging systems provide no mechanism for direct subscriber response to a page. Most pages require some sort of response, but, in the current art, the subscriber must employ an alternative means of communication (e.g. a telephone call) to supply a response.
c) Page message lengths are constrained to tens of bytes, limiting the utility of the paging system for detailed or lengthy messages.
Deficiencies (a) and (b), above, stem from the unidirectional nature of the message flow in the system. Deficiency (c) stems from the paging provider's business need to serve a large number of customers in combination with limited spectrum availability and an omnidirectional radio transmission strategy.